A Teleost is one of three infraclasses of Actinopterygii, the ray-finned fishes. In real life this diverse group, which arose in the Triassic period, includes 26,840 extant species in about 40 orders and 448 families; most living fishes are members of this group.

Teleosts have a movable maxilla and premaxilla and corresponding modifications in the jaw musculature. These modifications make it possible for teleosts to protrude their jaws outwards from the mouth. The caudal fin is homocercal, meaning the upper and lower lobes are about equal in size. The spine ends at the caudal peduncle, distinguishing this group from those in which the spine extends into the upper lobe of the caudal fin, such as most fish from the Paleozoic. Teleosts also have chloride cells which pump excessive sodium and chloride ions out into the sea.

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